One factor in assuring high print quality of inkjet printers is the control over the uniformity of ejected ink drops. Ink drop uniformity can be controlled by managing the temperature developed in heating elements, such as resistors, of the printhead. The heating elements reach high temperatures in order to produce explosive vaporization when vaporizing the ink. Some properties of an ink drop vary with temperature and there is an optimal temperature operating range for typical printheads using inks.
A heat-related problem can occur when the controller fires a heating element a number of times in a short period of time. This causes the heating element to reach a temperature that is higher than that required to produce ink drops having the correct size. Also, if the length of the current pulse to the resistor is longer than a pre-determined limit, the temperature of the heating element will again be too high for producing an ideal ink drop.
Another problem that can occur if the temperature at the heating element gets too high is that the gas formed will create bubbles that will choke the nozzle. In contrast, if the temperature is too low, the formation of ink droplets will be poor leading to a decrease in image quality of the image formed as these droplets are deposited on the print medium. These variations in drop weight, or the creation of bubbles, result in visible hue shifts and image quality defects.
Another potential problem caused by excessively high temperatures is that ink dyes can decompose leaving residues on the resistor surface. These residues can interfere with nucleation and drop formation, which can result in ink droplets with lower drop weight and lower velocity. This often causes print quality problems.
The present invention includes as one embodiment an inkjet printing system, comprising a substrate, a plurality of heating elements disposed on the substrate, an ink ejection assembly adjacent the substrate forming a plurality of ink ejection chambers, each chamber associated with a different one of the heating elements and a controller operatively connected to the heating elements, the controller receiving print data and processing the print data to predict thermal conditions of a subset of the ink ejection chambers for selectively operating the corresponding heating elements of the subset.